What will I miss in Arch64?

Nothing, really. Almost all applications support 64-bit by now or are in the transition to become 64-bit compatible.

These applications were previously problematic, but are now available in the AUR and work fine:

Skype as bin32-skype

Wine as bin32-wine

Zsnes as bin32-zsnes

The biggest problem are packages that are either closed source or contains x86-specific assembly that is cumbersome to port to 64-bit (typical for emulators).

TeamSpeak will not support 64-bit until the next version is released.

Flash player is not as smooth in 64-bit (youtube videos might be choppy)

Acrobat Reader plugin is not available in 64-bit, but you can run the 32-bit version in compatibility mode

Everything else should work perfectly fine. If you miss any Arch32 package in our port and you know that it will compile on x86_64 (perhaps you have found it as native packages in another 64-bit distribution), just contact the devs or request a new package in the forums.

Can I build 32-bit packages for i686 inside Arch64?

Yes. You need a working i686 chroot (installation with i686 iso "quickinstall" is recommended for the quick way to install it inside Arch64 or see Arch64 Install bundled 32bit system). Install "linux32" wrapper pkg from current to make the chroot behave like a real i686 system. Then use this script to login into the chroot environment as root:

Some 32-bit apps (like OpenOffice) may require additional bindings. The following lines can be placed in rc.local to ensure you get all you need for the 32-bit apps (assuming /mnt/arch32 is mounted in fstab):